SC follows the federal rules on the sale of you primary home. So, the first $250,000 ($500K Married filing jointly) of you gain is not taxed (excluded). Reference: https://www.listingsincharleston.com/blog/2022/9/19/south-carolina-real-estate-capital-gains-tax-exp....
As others have said, your cost basis is not $1. It's your mother's cost basis*.
"Gift Tax" is somewhat of a misnomer. Even though a gift tax return may be required, for your mother, for 4 years ago, very few people ever actually pay federal gift tax. The purpose of the gift tax return is usually only to document a reduction in the allowable estate tax exemption.
See https://turbotax.intuit.com/tax-tools/tax-tips/Tax-Planning-and-Checklists/The-Gift-Tax-Made-Simple/...
*There is an exception to your cost basis being her cost basis, if the house was worth less then her cost basis, on the date of the gift. But the exception seldom applies.
